The present invention relates generally to fastener-driving tools used to drive fasteners into workpieces, and specifically to combustion-powered fastener-driving tools, also referred to as combustion tools. More particularly, the present invention relates to improvements in a device or assembly that adjusts the depth-drive of the tool.
As exemplified in Nikolich, U.S. Pat. Re. Ser. No. 32,452, and U.S. Pat. Nos. 4,552,162; 4,483,473; 4,483,474; 4,404,722; 5,197,646; 5,263,439; 5,558,264 and 5,678,899 all of which are incorporated by reference, fastening tools, and particularly, portable combustion-powered tools for use in driving fasteners into workpieces are described. Such fastener-driving tools are available commercially from ITW-Paslode (a division of Illinois Tool Works, Inc.) of Vernon Hills, Ill., under the IMPULSE® and PASLODE® brands.
Such tools incorporate a tool housing enclosing a small internal combustion engine. The engine is powered by a canister of pressurized fuel gas, also known as a fuel cell. A battery-powered electronic power distribution unit produces the spark for ignition, and a fan located in the combustion chamber provides for an efficient combustion within the chamber, and facilitates scavenging, including the exhaust of combustion by-products. The engine includes a reciprocating piston having an elongate, rigid driver blade disposed within a piston chamber of a cylinder body.
The wall of a combustion chamber is axially reciprocable about a valve sleeve and, through a linkage, moves to close the combustion chamber when a workpiece contact element at the end of a nosepiece connected to the linkage is pressed against a workpiece. This pressing action also triggers a fuel-metering valve to introduce a specified volume of fuel gas into the closed combustion chamber from the fuel cell.
Upon the pulling of a trigger, a charge of gas in the combustion chamber of the engine is ignited, causing the piston and driver blade to be shot downward to impact a positioned fastener and drive it into the workpiece. As the piston is driven downward, a displacement volume enclosed in the piston chamber below the piston is forced to exit through one or more exit ports provided at a lower end of the cylinder. After impact, the piston returns to its original, or “ready” position through differential gas pressures within the cylinder. Fasteners are fed into the nosepiece from a supply assembly, such as a magazine, where they are held in a properly positioned orientation for receiving the impact of the driver blade. The power of these tools differs according to the length of the piston stroke, volume of the combustion chamber, fuel dosage and similar factors.
Combustion-powered tools have been successfully applied to large workpieces requiring large fasteners, such as for framing, roofing and other heavy-duty applications. Smaller workpiece and smaller fastener trim applications demand a different set of operational characteristics than the above-identified heavy-duty applications. Other types of fastener-driving tools such as pneumatic, powder activated and/or electrically powered tools are well known in the art, and are also contemplated for use with the present depth-of-drive adjustment assembly.
One operational characteristic required in fastener-driving applications, particularly in trim applications, is the ability to predictably control fastener-driving depth. For the sake of appearance, some trim applications require fasteners to be countersunk below the surface of the workpiece, others require the fasteners to be sunk flush with the surface of the workpiece, and some may require the fasteners to stand off above the surface of the workpiece. Depth adjustment has been achieved in pneumatically powered and combustion powered tools through a tool controlling mechanism, known as a drive probe, which is movable in relation to the nosepiece of the tool. Its range of movement defines a range for fastener depth-of-drive. Similar depth-of-drive adjustment mechanisms are known for use in combustion-type framing tools.
A conventional arrangement for depth adjustment involves the use of respective overlapping plates or tongues of a workpiece contact element and an upper probe or wire form. At least one of the plates is slotted for sliding relative to length adjustment. Threaded fasteners such as cap screws are employed to releasably secure the relative position of the plates together. The depth-of-fastener-drive is adjusted by changing the length of the workpiece contact element relative to the upper probe. Once the desired depth is achieved, the fasteners are tightened.
It has been found that users of such tools are inconvenienced by the requirement for an Allen wrench, nut driver, screwdriver or comparable tool for loosening the fasteners, and then retightening them after length adjustment has been completed. In operation, it has been found that the extreme shock forces generated during fastener-driving cause the desired and selected length adjustment to loosen and vary. Thus, the fasteners must be monitored for tightness during tool use.
To address the problem of maintaining adjustment, grooves or checkering have been added to the opposing faces of the overlapping plates to increase adhesion when the fasteners are tightened. However, to maintain the strength of the components in the stressful environment of fastener driving, the grooves must be made deep enough to provide the desired amount of adhesion. Deeper grooves could be achieved without weakening the components by making the plates thicker, but that would add weight to the linkage, which is undesirable.
Other attempts have been made to provide tool-free depth-of-drive adjustment, but they have also employed the above-described opposing face grooves for additional adhesion, which is still prone to the adhesion problems discussed above.
Another design factor of such depth adjustment or depth-of-drive (used interchangeably) mechanisms is that the workpiece contact elements are often replaced over the life of the tool. As such, the depth adjustment mechanism preferably accommodates such replacement while retaining compatibility with the upper probe of the tool, which is not necessarily replaced.
Accordingly, there is a need for an improved fastener-driving tool depth-of-drive adjustment assembly where the adjustment is secured without the use of tools and is maintained during extended periods of fastener driving. There is also a need for an improved fastener depth adjustment assembly which provides for more positive fastening of the relative position of the workpiece contact element without reducing component strength. Finally, there is a need for an improved fastener depth-of-drive assembly which can be replaced when the life of the workpiece contact element has expired without requiring the replacement of the entire fastener-driving tool.